Giant Flyers: to the limit (or not)

I am preparing for my departure to the Experimental Biology Conference in San Diego (starts today), so another brief post today.

One of my pet projects over the last couple of years has been to make a go at estimating the maximum mechanically allowed size for each of the groups of  powered vertebrate flyers: birds, bats, and pterosaurs.  This is a rather difficult task for many reasons, not the least being that working out the "weak link" in any given scaling problem is time consuming.  Pterosaurs provide a special challenge since they provide no living representatives to work on.

I have a preliminary model now, however, and I am rather excited about it.  Because it's still rough, I am not going to get into too much detail, but here are some of the punchlines if I turn out to be right with my approach (emphasis on "if"):

- None of the flying clades ever produced an animal at the mechanical flight limit for the group, which means that ecological limits or other constraints have historically set the maximum size.

- Of the three clades, birds came the closest to reaching their mechanical limit (Argentavis)

- Giant pterosaurs, even though they were the largest flying animals, were further from their mechanical limit than the largest flying birds.

- Bats have the lowest absolute limit, but they also have the greatest gap between observed max size and potential max size.  As a result, ecological constraints on size might be particularly strong for bats.  A 3 meter wingspan bat does not seem impossible with the numbers I have right now.  That would more than double the maximum span of the largest bat on record.

All of these limits are estimated using the most giant-friendly morphology in each clade: teratorns for birds, azhdarchids for pterosaurs, and megachiropterans for bats.  There could be altogether novel morphologies out there for each group that would push the limit higher, though for various reasons I can get into later, I think the limits I am calculating are somewhat generalizable.